The present invention relates to resonant tags and more particularly to a process for making resonant frequency circuits for use as resonant tags.
Resonant tags are tags which include a passive electrically resonant frequency circuit which resonates at a predetermined frequency when stimulated by a radio frequency electromagnetic field at about the resonant frequency of the tag and which is incident upon the resonant tag. The resonant frequency circuit resonating within a region occupied by the electromagnetic field perturbs the electromagnetic field. The perturbation of the electromagnetic field is detectable by suitable equipment. Consequently, the presence of a resonant tag within a prescribed region may be detected.
Typically, resonant tags are attached to goods sold at retail in order to deter theft. Resonant tags used for this purpose are capable of being removed from the goods or deactivated when a legitimate sale is consummated. Resonant tags which are not removed or deactivated at the point of sale may be detected by suitable detection apparatus, generally placed at points of exit from a retail establishment.
Typically, a resonant tag comprises a generally flat thin laminate of a dielectric layer separating conductor layers. Typically, one of the conductor layers comprises a flat spiral conductor (coil) forming an inductance, and one plate of a capacitor connected to a proximal end of the coil. A second plate of the capacitor is formed on the second conductor layer. A through connection between the second plate and a distal end of the coil completes the resonant frequency circuit comprising the coil inductor and the capacitor.
It is required that the inductive and capacitive elements of resonant tags be manufactured with precision in order that the resonant frequency of the tags be held within prescribed limits. A generally used method for making resonant tags employs etching a metallic foil to form the components of the conductive layers. This process, while yielding the necessary precision, results in excessive waste of the metallic foil.
Accordingly, it would be desirable to have a process for making resonant tags which maximizes the yield of completed tags and minimizes waste material resulting from making the tags.